1. Field of the Invention
The present invention relates to an automatically reset control mechanism for implementing the playback under remote control of incoming messages recorded by a telephone answering device.
2. Description of the Prior Art
A telephone answering device having remote controlled playback enables a user to obtain his messages without returning to the physical location of the answering device. To accomplish this, the user places a telephone call to his own number. The call is answered automatically by the answering device. At an appropriate time during the answering cycle the user transmits a coded signal, for example, a "beep" tone produced by a small oscillator that is held against the telephone handset microphone. The telephone answering device recognizes this specific signal, and switches to the automatic playback mode. The incoming message tape is rewound, and the recorded messages then are played back over the telephone line to the user. When all of the messages have been played out, the device is reset to the answering mode and shut down in readiness to receive the next call.
A cam control mechanism advantageously is used in such a device to implement automatic rewinding of the tape and transfer of the tape drive mechanism to the forward direction for playout of the recorded messages. Such mechanisms are taught e.g., in the inventor's U.S. Pat. No. 4,104,487 and No. 4,126,763 as well as in the inventor's copending U.S. patent applications, Ser. No. 879,279 filed Feb. 21, 1978, now U.S. Pat. No. 4,197,426 issued Apr. 8, 1980, No. 925,370 filed July 17, 1978, now U.S. Pat. No. 4,213,010 issued July 15, 1980, No. 941,282 filed Sept. 11, 1978, now U.S. Pat. No. 4,201,886 issued May 6, 1980, and No. 27,911 filed Apr. 6, 1979.
In these systems, a cam is used to transfer the motor, which drives the incoming message tape, between forward and rewind drive positions. In the ready condition, the tape drive motor is positioned for forward tape motion. Upon receipt of a "beep" tone or other remote playout control signal, the cam drive motor rotates the cam so as to transfer the tape drive motor to the rewind position. The cam remains so situated until rewind is complete. The cam mechanism then is reactuated to return the tape drive motor to the forward position, so that the messages can be played out.
A problem exists with such cam control mechanisms. In the event of a power interruption during the changeover cycle, the cam mechanism may be left in an improper orientation. For example, the tape drive motor may be left in the rewind position. After power is restored, during the next answering cycle the incoming message tape will be driven improperly in the reverse direction. As another example, the power interrupt may occur as the cam mechanism is in the midst of transferring the tape drive motor. In this instance, when power later is applied during an answering cycle, the outgoing announcement tape may not be moved at all. As a third example, the tape drive motor may be in the forward position, but with the cam rotated sufficiently so as to disengage the control switch associated with the cam mechanism. In such instance a normal answering cycle may be implemented, but proper remote controlled playout will not be possible.
Thus it is a principle object of the present invention to provide a cam control mechanism that is automatically restored to the correct ready position when power is applied to the telephone answering device, if the orientation at that time is incorrect. The cam orientation is sensed, and the cam drive motor is energized if necessary so as to return the cam mechanism to the correct position.
In some known telephone answering devices, solenoids are used to position the tape drive motor. Such solenoids automatically return the tape drive motor to the proper rest condition when de-energized, and therefore do not have the inherent shortcoming which the present invention eliminates. Another object of the present invention is to simulate solenoid operation by providing an improved cam control mechanism which automatically correctly repositions the tape drive motor after a power interrupt, but without the use of solenoids.
During operation of the cam control mechanism it is necessary to determine when rewinding of the incoming message tape is complete. One technique is to employ a feeler switch which is actuated when the tape on the supply reel reaches a certain diameter. This technique is inaccurate because the tape diameter may vary somewhat depending on whether the tape is more tightly or loosely wound onto the spool during rewind. Thus if the tape is loosely wound, the feeler switch may close prematurely, before all of the tape has actually been rewound onto the supply reel.
Another technique for sensing that rewind is complete is to provide an electrically conductive strip on the message tape near the leading end thereof. Completion of rewind then can be detected when this conductive strip shorts together a pair of contacts physically situated along the tape path near the supply reel. Still another method is to sense the increased drag on the motor caused by the greater tape tension when rewind is complete. A further method is shown in the U.S. Pat. No. 3,991,274 to Darwood. There a microswitch is eccentrically connected to the feed spindle of the message tape drive mechanism so as to be intermittently opened and closed as the tape is rewound. The resultant pulses produced by the microswitch are sensed by a circuit which produces an end-of-rewind signal when the pulses terminate. These techniques, however, require additional circuitry or mechanisms that add to the cost of the device.
Another object of the present invention is to provide a means for detecting the end of rewind of the incoming message tape by monitoring the audio output of that tape during rewind. Termination of such audio indicates that rewind is complete.
A further object is to provide an alternative means for detecting the end of rewind by monitoring the brush noise from a tightly coupled message tape drive motor. When the motor stalls at the end of rewind, the brush noise terminates to indicate rewind completion.